In modern commercial aircraft, the demand for as high a cruising speed as possible coupled with as low a takeoff and landing speed as possible is giving rise to the necessity of high lift systems, which can be activated during takeoffs and landings to markedly increase the lift coefficient. This is generally accomplished with lift-increasing flaps, which are deflected into the air stream of the aircraft. Among other things, especially widespread use is made of an abundance of different slats, e.g., extensible slats (“extensible slat”) or leading edge flaps, such as Krüger flaps (“Kruger flap”), which are arranged so that they can move relative to the wing. For the sake of simplicity, the slats and flaps will be generally referred to as “lift flaps”.
In one or several extended positions, lift flaps designed as slats can be spaced or offset away from the leading edge of the wing, thereby forming a gap relative to the leading edge of the wing. The gap allows an energy-rich stream of air to move from the flow approaching the wing onto the upper profile side of the wing, where it shifts the stall toward higher angles of attack. Depending on the design, lift flaps can be deflected with or without forming a gap in the flow approaching the aircraft, and increase both the surface of the wing and its curvature.
To ensure that the wing contour comprises a contour optimized for cruising flight with the lift flaps in a retracted position, the wing comprises depressions, recesses, indentations or the like for accommodating the lift flaps, wherein the shape of the lift flaps and depressions in the wing are adjusted to each other. As a consequence, the combination of wing and lift flaps gives rise to the outward cruising flight contour with the lift flaps retracted. Given a lift flap mounted so that it can pivot around an axis in the area of the leading edge of the wing, one section of a cruising flight contour for the bottom side of the wing yields the upper contour of the lift flap in the extended state.
Lift flaps are usually rigid, and comprise an internal structural design. How the surface of the lift flap directed relative to the wing in a stowed position is formed is essentially determined by this internal structural design, and hence prescribes the size of the corresponding depression for stowage in or on the wing. The lift flaps often comprise a tapering structural thickness, so that the depression in the wing is configured to correspond thereto.
DE 10 2006 053 259 A1 and WO 2008/058695 A1 introduce a high lift system for a wing of an aircraft in which lift flaps can be moved from a retracted position to extended positions in order to increase lift, wherein a gap between the high lift flaps and wing can be opened or closed independently of the position of the high lift flaps. This makes it possible to optionally achieve an improved maximum lift coefficient or improved drag ratio with less noise being generated.